This invention relates to reinforced polyethylene terephthalate molding compositions.
Polyethylene terephthalate molding compositions which are reinforced with glass fibers, asbestos fibers, or other fibrous mineral material are known to either crystallize slowly and give molded articles with a resin rich glossy surface finish, inferior mechanical properties and slow molding cycles, or to rapidly crystallize, giving molded articles with good mechanical properties and short molding cycles but low gloss surface finish. One method of improving surface gloss is to increase the mold temperature but this can result in longer cooling times. It is also known that molding wet polyethylene terephthalate produces parts with good gloss but poor mechanical properties.
It is difficult to make fiber reinforced polyethylene terephthalate molding compositions which will rapidly crystallize and which give molded articles which display high surface gloss and good physical and mechanical properties. Processability, shorter cycle times and better flow properties are important. Thus, even when a particular polyethylene terephthalate molding composition is molded into articles which display both good surface finish characteristics and some good strength characteristics, the articles may not possess the combination of thermal, electrical and mechanical properties required for many commercial applications. For example, in engineering resin applications, a glass fiber reinforced polyethylene terephthalate molding composition needs to have good spiral flow and rapid crystallization; it should provide molded articles with attractive surface appearance, high heat distortion temperature and minimal warpage after the part is removed from a mold.
There is a need for reinforced polyethylene terephthalate molding compositions from which can be made articles with high surface gloss and engineering resin performance characteristics. Also, there is a need for compositions of this type which display high flow rates under molding conditions without water addition and without lubricant addition. In addition, these compositions should also be capable of having a flame retardant material added thereto in an amount effective for achieving flame retardancy without a significant change in the combination of properties exhibited by articles molded from the composition. There is also a need for compositions of this type which can be colored without significantly changing properties of the composition or articles molded from the composition while retaining good processability.